As thousands of honeybee hives have collapsed in the last several years, researchers have struggled to identify the cause. Now, new research may indicate an unusual suspect: Parasitic flies.

Colony collapse disorder has decimated wild and farmed honeybee populations in the U.S. Critical for the pollination of a number of fruits and vegetables—some $15 million worth annually—making the loss of functional pollinator and honey-making beehives devastating for the nation’s food producers.

Now, a new study conducted by San Francisco State University researchers points to a parasitic fly (Apocephalus borealis) common in North America that makes the bees become disoriented and eventually killing them. More than 75 percent of hive sites in the San Francsico Bay area and in hives in South Dakota have shown the presence of the parasitic flies.

While the researchers do not think the fly infestations are the sole cause of the widespread colony collapse disorder, it’s most definitely a cause for concern, says the scientists involved, and warrants more research and a recommendation that preventative measures by honeybee farmers be explored.

According to the USDA’s website, “the main symptom of CCD is simply no or a low number of adult honey bees present but with a live queen and no dead honey bees in the hive. Often there is still honey in the hive, and immature bees (brood) are present.” A number of additional factors have been considered culprits in CCD without any conclusive findings, including electromagnetic frequencies from cell phones, inexplicable viruses and other parasites such as mites, and exposure to genetically modified foods and pesticides.